We describe the design, construction, and operation of the Carnegie Observatories Spectroscopic Multislit and Imaging Camera (COSMIC) for the prime focus of the Hale 5 m telescope at Palomar Observatory. COSMIC is a reimaging grism spectrograph with a 13.65 arcmin square field of view, which can also be used as a direct imaging camera with a 9.75 arcmin square field of view. The wavelength coverage extends from 350 nm to almost 1 mm; the detector is a thinned, back-illuminated SITe CCD with high quantum 2048 # 2048 efficiency and excellent cosmetics. Multislit aperture masks are produced photographically, with spectra of up to ∼50 objects fitted on a single row of a slit mask. The instrument exhibits very little flexure and uses an active thermal control to maintain focus over a wide range of ambient temperature. In direct mode COSMIC is typically used with Kron-Cousins, Gunn, and narrow bandpass filters. The instrument achieves throughputs of greater than 50% for direct imaging and, in spectroscopic mode, a peak efficiency at 5500 A ˚of slightly better than 24% of light falling on the 5 m mirror. COSMIC is optimized for faint-object imaging, down to Gunn mag, and r ϭ 26 multiobject spectroscopy, down to mag, with typically 30 objects per spectroscopic exposure. r ϭ 23

Epitaxial ferromagnetic metal -semiconductor heterostructures are investigated using polarization-dependent electroabsorption measurements on GaAs p-type and n-type Schottky diodes with embedded In 1-x Ga x As quantum wells. We have conducted studies as a function of photon energy, bias voltage, magnetic field, and excitation geometry.For optical pumping with circularly polarized light at energies above the band edge of GaAs, photocurrents with spin polarizations on the order of 1 % flow from the semiconductor to the ferromagnet under reverse bias. For optical pumping at normal incidence, this polarization may be enhanced significantly by resonant excitation at the quantum well ground-state. Measurements in a side-pumping geometry, in which the ferromagnet can be saturated in very low magnetic fields, show hysteresis that is also consistent with spin-dependent transport. Magneto-optical effects that influence these measurements are discussed.

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The optical, mechanical, and electronic designs of a multipurpose near-infrared ( 1.1-2.5 pm) camera built for Las Campanas Observatory are described. The camera is used on both the 2.5-m duPont and 1-m Swope Telescopes. A refractive all-spherical achromatic reimager incorporates three confocal discrete zooms which image onto a Rockwell HgCdTe (NICMOS2) 128 X 128 detector array. Although the instrument was designed primarily for imaging, we have included two experimental modes for future use-a low-resolution grism (R~400) and a coronagraph. The optical design choices and procedures are described in some detail. The entire 0.6 m optical path resides at 77 K and is folded onto a 25.4 cm diameter dewar work surface. The instrument is remotely controlled by a Sun 386i graphics workstation via serial links to microprocessor-controlled motor-encoder packages and the array control electronics. Electronic designs suitable for use with a NICMOS2 array are given. The data are acquired and inspected using IRAF routines running under the UNIX multitasking environment. Initial performance results on camera optical quality and system sensitivity are given.

Optical pumping is used to generate spin-polarized carriers in epitaxial ferromagnet-GaAs Schottky diodes with In y Ga 1Ϫy As quantum wells placed in the depletion region. A strong dependence of the photocurrent on the polarization state of the incident light is observed, and a series of measurements as a function of excitation energy, bias voltage, magnetic field, and excitation geometry are used to distinguish spin-dependent transport from a variety of background effects. The spin polarization of the photocurrent for pumping energies at and above the band gap of GaAs is of order 0.5% or less. Much larger polarization dependence is observed for excitation energies near the quantum well ground state. Although background effects are very large in this regime, the field dependence of the polarization signal for several samples is suggestive of spin-dependent transport.